(N/A) The migratory pattern of birds is one of the mysteries in the field of biology and indeed all of science.
For example,every winter,birds from Siberia fly unerringly to water bodies in the Indian subcontinent. It has been suggested that electromagnetic induction may provide a clue to these migratory patterns.
The Earth's magnetic field has existed throughout evolutionary history.
It would be of great benefit to migratory birds to use this field to determine their direction.
As far as we know,birds contain no ferromagnetic material. So,electromagnetic induction seems to be the only reasonable mechanism to determine direction.
Consider the optimal case where the magnetic field $\vec{B}$,the velocity of the bird $\vec{v}$,and two relevant points of its anatomy separated by a distance $l$ are all mutually perpendicular. From the formula for motional $EMF$,$\varepsilon = B l v$.
Taking $B = 4 \times 10^{-5} \ T$,$l = 2 \ cm = 2 \times 10^{-2} \ m$,and $v = 10 \ m/s$,we obtain:
$\varepsilon = (4 \times 10^{-5}) \times (2 \times 10^{-2}) \times 10 \ V = 8 \times 10^{-6} \ V = 8 \ \mu V$.
This extremely small potential difference suggests that our hypothesis is of doubtful validity.
Certain kinds of fish are able to detect small potential differences. However,in these fish,special cells have been identified which detect small voltage differences. In birds,no such cells have been identified. Thus,the migration patterns of birds continue to remain a mystery.